How to Tell If Miso Has Gone Bad

If you have leftover miso paste that hasn’t been used for a while and are wondering whether to toss or use for cooking… read on for tips about how long miso paste lasts and everything else you need to know!

Miso Paste

Miso paste is a traditional Japanese condiment made from fermenting soybeans, koji, and salt. It adds a complex and unique umami flavor not only to miso soup but also to dressings, stir-fry sauces, and various dishes. To learn more, check out “What Is Miso Paste and How To Use It: A Beginner’s Guide.”

How Long Does Miso Last?

Traditional miso paste has a remarkably long shelf life, typically ranging from 3 months to 12 months, depending on the variety. This extended freshness is primarily due to the high salt content in miso, which acts as a preservative, ensuring that the miso stays fresh for an extended period.

While miso paste doesn’t go bad easily, its taste can deteriorate over time. However, it’s important to be aware that low-salt or processed miso varieties, especially those with added soup stock, might be more likely to go bad.

For Example

As I mentioned earlier, the shelf life of miso paste can vary depending on the type of miso paste. Here are some examples of expiration dates:

White miso paste: 6 months
Red miso paste: a year
Reduced sodium miso paste: 6 months
Homemade miso paste: a year or more

Signs of Spoilage

How do you know if a miso paste is bad? Since it’s a fermented food, it continues to develop its flavor. If it’s not stored correctly, you might see some signs of going bad. Is this bad? Is this OK to eat? Here are some samples you might run into if you haven’t used miso for a while.

Check These for Spoilage Signs

1. The Color is Darker than Before: You may find your miso paste is darker than before, and wonder if this is ok to eat. The longer the time passes, the more miso’s color changes and gets darker (called the Maillard reaction). Darker miso is matured. So it’s natural as fermentation goes on all the time. The taste also changes to a less sweet and deeper flavor. Some people love this aged miso flavor, and some prefer a light and sweeter one. If you like the taste of dark color miso or mature miso, you can keep using it.
2. It Tastes Sour: If your miso has a sour taste, it is likely due to the fermentation process going on for too long. You can still eat it, but it doesn’t taste good. It’s probably best to avoid consuming it.
3. White Mold Grows: It’s common to encounter white fluffy mold on miso paste, but you don’t need to panic. It only grows on the surface of the miso, so you remove about an inch from where the mold is growing; after that, you can eat it safely. However, if you use reduced sodium miso or the one with dashi stock, be careful – these molds could indicate going bad. If it smells strange, it would be better to throw it away.
4. Smells Bad: When you realize that it smells different…if it smells like alcohol, it’s okay because a small amount of alcohol occurs during fermentation. If it smells strange or wrong, you should stop using it.

Can You Use Miso Paste Past the Expiration Date?

Yes, you can, but it may not depend on how it’s stored. Even though it has a best-by date, as a preservative food, it lasts way beyond the date and can be enjoyed over time.

However, suppose it is stored in a warm environment for a long time. In that case, you might see some deterioration in miso paste as heat and high humidity speed up the fermentation process.

How to Store Miso Paste

Where is the best place to store miso paste? Storage conditions are critical to keeping good-quality fresh miso. The best way is to keep it at low temperatures. So, I highly recommend putting it in an airtight container and storing it in the fridge.
Even unopened miso keeps fermenting, so storing it in the fridge is also better.
If the surface of the miso dries up in the refrigerator, cover it with plastic wrap and close the lid.
If you prefer to store miso at room temperature, keep it in a cool, dark place, like kitchen cabinets. (Room temperature should be less than 25 degrees.)
Click here for a complete guide on How to store miso paste.

The Best Way to Use Old Miso Paste

If your miso paste is not so fresh, but you don’t want to toss it, here are the best ways to use up your old miso!

Miso mayo: Mix miso paste and mayonnaise. Use it as a dipping sauce for vegetable sticks.
Miso salad dressing: Mix miso paste, vinegar, sugar, and olive oil and make a salad dressing.
Misozuke (pickle): Make a pickling mixture with miso paste and mirin. Pickle vegetables (carrot, daikon, cucumber, etc.) or tofu overnight.
Stir fry: Make a mixture with miso paste, soy sauce, and mirin. Use it as stir-fry seasoning.